Patients with Postural Tachycardia Syndrome (POTS) may not adequately expand their plasma volume in response to a high sodium diet. Mechanisms involved in the regulation of plasma volume, such as the renin-angiotensin-aldosterone system and renal dopamine (DA), may be impaired in POTS and may respond inappropriately to changes in dietary sodium. The investigators propose that the changes in urinary sodium and dopamine excretion caused by consuming low-sodium and high-sodium diets will be different between patients with POTS and healthy volunteers. The purpose of this study is to determine (1) whether changes in dietary sodium level appropriately influence sodium excretion in POTS; (2) whether changes in dietary sodium level appropriately influence DA excretion in POTS; (3) whether a high dietary sodium level appropriately expands plasma volume in POTS; and (4) whether patients with POTS have improvements in their orthostatic tachycardia and symptoms as a result of a high dietary sodium level.

subjects breath room air through a mouthpiece and exhale the air into a tube that connects to a machine (metabolic cart) that analyzes carbon dioxide and oxygen content, which allows the investigator to calculate the amount of oxygen they are using under resting and exercise conditions.

Other Name: VO2 Max (maximal oxygen consumption)

Procedure: Posture Study

Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes. Blood will be drawn in each position to measure hormones that regulate blood pressure and blood volume.

subjects breath room air through a mouthpiece and exhale the air into a tube that connects to a machine (metabolic cart) that analyzes carbon dioxide and oxygen content, which allows the investigator to calculate the amount of oxygen they are using under resting and exercise conditions.

Other Name: VO2 Max (maximal oxygen consumption)

Procedure: Posture Study

Blood pressure and heart rate will be measured while supine and then while standing for up to 30 minutes. Blood will be drawn in each position to measure hormones that regulate blood pressure and blood volume.

This will be done after supine assessment, but before standing the subject up

Exercise Capacity Test (in the afternoon) Will estimate maximal oxygen consumption (VO2 max) This test will be conducted on a stationary bicycle. Effort will be gradually increase while expired air is measured during exhaustive physical work.

All procedures are repeated at least a month later with the 2nd level of dietary salt. (Randomized to high or low salt in the first phase, the second phase is the remaining level)

Eligibility

Ages Eligible for Study:

18 Years to 50 Years (Adult)

Genders Eligible for Study:

Female

Accepts Healthy Volunteers:

Yes

Criteria

Inclusion Criteria:

Premenopausal patients with POTS and healthy volunteers, 18-50 years old, who are non-smokers and free of medications with the potential to influence blood pressure

Increase in heart rate ≥30 beats/min with position change from supine to standing (10 minutes)

Chronic symptoms consistent with POTS that are worse when upright and get better with recumbence

Only female participants are eligible. Since 80-90% of POTS patients are female, and there can be differences in measures with the menstrual cycle, including a small number of males might introduce a significant amount of noise.

Able and willing to provide informed consent

Exclusion Criteria:

Smokers

Overt cause for postural tachycardia, i.e., acute dehydration

Significant cardiovascular, pulmonary, hepatic, or hematological disease by history or screening results

Positive pregnancy test or breastfeeding

Hypertension defined as BP>145/95 off medications when supine or needing antihypertensive medication

Other factors which in the investigator's opinion would prevent the participant from completing the protocol, including poor compliance during previous studies or an unpredictable schedule

Unable to give informed consent

Contacts and Locations

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01563107